feat: K线数据使用Decimal类型，防止数值精度丢失和溢出

flutter_monisuo/lib/models/candle.dart

@@ -1,11 +1,13 @@
+import 'package:decimal/decimal.dart';
+
 /// K 线数据模型
 class Candle {
   final int timestamp; // 毫秒时间戳
-  final double open;
-  final double high;
-  final double low;
-  final double close;
-  final double volume;
+  final Decimal open;
+  final Decimal high;
+  final Decimal low;
+  final Decimal close;
+  final Decimal volume;
 
   const Candle({
     required this.timestamp,
@@ -16,23 +18,82 @@ class Candle {
     required this.volume,
   });
 
+  /// 从 JSON 解析，使用 Decimal 避免精度丢失
   factory Candle.fromJson(Map<String, dynamic> json) {
     return Candle(
       timestamp: json['timestamp'] as int? ?? json['time'] as int? ?? 0,
-      open: (json['open'] as num?)?.toDouble() ?? 0,
-      high: (json['high'] as num?)?.toDouble() ?? 0,
-      low: (json['low'] as num?)?.toDouble() ?? 0,
-      close: (json['close'] as num?)?.toDouble() ?? 0,
-      volume: (json['volume'] as num?)?.toDouble() ?? 0,
+      open: _parseDecimal(json['open']),
+      high: _parseDecimal(json['high']),
+      low: _parseDecimal(json['low']),
+      close: _parseDecimal(json['close']),
+      volume: _parseDecimal(json['volume']),
     );
   }
 
+  /// 安全解析 Decimal
+  static Decimal _parseDecimal(dynamic value) {
+    if (value == null) return Decimal.zero;
+    if (value is Decimal) return value;
+    if (value is num) return Decimal.fromJson(value.toString());
+    if (value is String) {
+      try {
+        return Decimal.parse(value);
+      } catch (_) {
+        return Decimal.zero;
+      }
+    }
+    return Decimal.zero;
+  }
+
   Map<String, dynamic> toJson() => {
         'timestamp': timestamp,
-        'open': open,
-        'high': high,
-        'low': low,
-        'close': close,
-        'volume': volume,
+        'open': open.toDouble(),
+        'high': high.toDouble(),
+        'low': low.toDouble(),
+        'close': close.toDouble(),
+        'volume': volume.toDouble(),
       };
+
+  /// 转换为 double（供图表库使用）
+  double get openDouble => open.toDouble();
+  double get highDouble => high.toDouble();
+  double get lowDouble => low.toDouble();
+  double get closeDouble => close.toDouble();
+  double get volumeDouble => volume.toDouble();
+
+  /// 安全加法（防止溢出）
+  Decimal safeAdd(Decimal other) {
+    try {
+      return open + other;
+    } catch (_) {
+      return Decimal.zero;
+    }
+  }
+
+  /// 安全乘法（防止溢出）
+  Decimal safeMultiply(Decimal other) {
+    try {
+      return open * other;
+    } catch (_) {
+      return Decimal.zero;
+    }
+  }
+
+  /// 格式化价格显示
+  String formatPrice({int decimalPlaces = 2}) {
+    return close.toStringAsFixed(decimalPlaces);
+  }
+
+  /// 格式化成交量显示
+  String formatVolume() {
+    final vol = volume.toDouble();
+    if (vol >= 1000000000) {
+      return '${(vol / 1000000000).toStringAsFixed(2)}B';
+    } else if (vol >= 1000000) {
+      return '${(vol / 1000000).toStringAsFixed(2)}M';
+    } else if (vol >= 1000) {
+      return '${(vol / 1000).toStringAsFixed(2)}K';
+    }
+    return vol.toStringAsFixed(2);
+  }
 }